in Pleß Bulgaria and Germany signed a treaty of alliance and a military convention that laid the plan for the conquest of Serbia and included Austria-Hungary as a third party,. In accordance with the said agreements Bulgaria concentrated against Serbia its First Army, as part of Army Group Mackensen and its Second Army which remained under the direct control of the Bulgarian High Command. The Second Army under Lieutenant General Todorov finished its concentration in the Kyustendil – Dupnitsa – Blagoevgrad area by 30 September. Its order of battle was as follows: The Serbians could oppose these forces with their Macedonian forces under general Damian Popovic. The total strength was 44 battalions with 16 batteries or in other words some 41,250 riflemen, 78 cannons and 38 machine guns. By 30 September however only 31 battalions with 11 batteries or 29,600 riflemen, 54 cannons and 24 machine guns were on the border with Bulgaria, the rest were guarding the border with Albania. The Serbians adopted a passive defense approach, hoping that their insufficient forces will hold out long enough for the Entente to reinforce them with the troops that were already landing in Salonika. The objectives of the Bulgarian Second Army were to cut the communication and supply lines between Macedonia and Serbia, to prevent a retreat of the main Serbian forces to Macedonia and to repel any Entente attempts to reinforce the Serbians from the south. On 1 October (14 October) 1915 Bulgaria declared war on Serbia and the Second Army was ordered to begin its attack drive towardsOvche Pole. The weak Serbian force were quickly defeated and forced to retreat from the border area with the Bulgarian forces taking Tsarevo Selo and Kriva Palanka followed on 16 October by the entry of the 2/3 Infantry Brigade in Vranje. On 6 October (20 October) the Bulgarian 3rd Division overwhelmed the Serbian positions at Stracin which allowed it to seize Kumanovo. This practically isolated Serbia from Macedonia and cut the communication and supply lines with Salonika. On 9 October after a brief fight the Bulgarians took Skopje. At the same time in the fighting near Krivolak and Strumitsa for the first time, French forces of the 156th division aided their Serbian allies by gradually replacing and allowing them to be transferred further to the west. On 10 October concerned by the Serbian and Entente efforts to join their forces in Macedonia